Gold(I) NHC catalysts immobilized to amphiphilic block copolymers: a versatile approach to micellar gold catalysis in water

Fifteen gold(I)-NHC-functionalized amphiphilic block copolymers that differ in the type of linker (ethyl, pentyl, octyl and benzyl) that attaches the gold(I) NHC catalyst to the block copolymer backbone, as well as, the substitution pattern of the NHC ligand (i. e. mesityl, methyl, 2,6-diisopropylphenyl and n-hexyl) were synthesized by a reversible addition and fragmentation transfer (RAFT) polymerization process. Micelle formation of the gold(I) NHC polymers was analyzed by electron microscopy and dynamic light scattering and revealed spherical and rod-like particles from 12 to 96 nm. In the micellar, gold(I) catalyzed cycloisomerization of an allene to the corresponding dihydrofuran, linker flexibility and substitution pattern of the NHC-ligand showed a strong effect on the catalytic activity. Best results were obtained were obtained for gold(I) NHC catalysts bound to the polymer backbone by pentyl linker whereas the rather stiff benzyl linker gave lowest catalyst conversion. Moreover, the polymer catalyst could be recycled in four consecutive runs and gave activities from 35 to 84 % in the fourth run and underscores the importance of fine tuning structural parameters to achieve high conversion under micellar reaction conditions

Efficient synthesis of macromolecular DO3A@Gn derivatives for potential application in MRI diagnostics: from polymer conjugates to polymer nanoparticles

Herein, the synthesis of three different macromolecular DO3A@Gn conjugates based on poly(2-oxazoline)s is presented. Therefore, poly(2-methyl-2-oxazoline) is synthesized by a ring-opening, cationic polymerization and the polymerization is terminated with DO3A(tBu)3. The best results are obtained after 48 h at 120 °C with degree of termination of 86%. After deprotection of the DO3A ligand and complexation with Gn3+, relaxivity as measured with a magnetic field strength of 9.4 T (400 MHz) reveals values for r1 of up to 2.32 mm−1 s−1. The concept is extended to a block copolymer based on 2-heptyl-2-oxazoline and 2-methyl-2-oxazoline that is again terminated with DO3A(tBu)3 to form micelles with a size of 12.6 ± 0.7 nm after DO3A(tBu)3 termination and deprotection of the 1,4,7,10-tetraazacyclododecane-N,N,N,N-tetraacetic acid ligand. After complexation with Gn3+, relaxivity r1 is 10.1 mm−1 s−1 as determined from the slope of the plot of 1/T1 against the gadolinium(III) concentration at 9.4 T. Finally, crosslinked nanoparticles are prepared from amphiphilic macro-monomers that form micelles in water and are crosslinked throughout the core in the presence of azoisobutyronitrile (AIBN). The nanoparticle is 32.9 ± 7.8 nm in size after Gn3+ complexation and reveals a relaxivity r1 of 6.77 mm−1 s−1

Synthesis of redox-responsive core–shell nanoparticles: insights into core-crosslinking efficiency

Core-crosslinked micelles have become an important class of materials for biomedical applications. However, there has been little work attempting to quantify the efficiency of the core crosslinking reaction, instead residual polymers are usually removed by dialysis. In this work we have prepared core crosslinked micelles based on poly(2-ethyl-2-oxazoline)-block-poly(n-butyl acrylate-co-D,L-homocysteine thiolactone acrylamide). Core crosslinking was examined by the addition of six different di- and triamines and nucleophilic ring-opening of the thiolactone ring. By using size exclusion chromatography (SEC) we were able to quantify the amount of crosslinked micelle and free block copolymer and were able to optimize the crosslinking conditions in terms of temperature, reaction time and crosslinker equivalents to obtain up to 80% core-crosslinked micelles. Subsequently, micelles that were crosslinked with cystamine were degraded in the presence of dithiothreitol (DTT) and resulted in degradation times of 1.5 h to 5 h and depended strongly on the composition of the hydrophobic core as shown by dynamic light scattering (DLS) and size exclusion chromatography (SEC). Cytotoxicity assays of the core-crosslinked micelles and block copolymer precursors were performed with COS7 cells and revealed high cell viabilities up to 0.1 mg mL−1

Synthesis and characterization of cationic hydrogels from thiolated copolymers for independent manipulation of mechanical and chemical properties of cell substrates

Cells sense both mechanical and chemical properties in their environment and respond to these inputs with altered phenotypes. Precise and selective experimental manipulations of these environmental cues require biocompatible synthetic materials, for which multiple properties can be fine-tuned independently from each other. For example, cells typically show critical thresholds for cell adhesion as a function of substrate parameters such as stiffness and the degree of functionalization. However, the choice of tailor-made, defined materials to produce such cell adhesion substrates is still very limited. Here, a platform of synthetic hydrogels based on well-defined thiolated copolymers is presented. Therefore, four disulfide crosslinked hydrogels of different composition by free radical polymerization are prepared. After cleavage with dithiothreitol, four soluble copolymers P1–P4 with 0–96% cationic monomer content are obtained. P1 and P4 are then combined with PEGDA3500 as a crosslinker, to fabricate 12 hydrogels with variable elasticity, ranging from 8.1 to 26.3 kPa and cationic group concentrations of up to 350 µmol cm−3. Systematic analysis using COS7 cells shows that all of these hydrogels are nontoxic. However, successful cell adhesion requires both a minimal elasticity and a minimal cationic group concentration

Towards DNA-encoded micellar chemistry: DNA-micelle association and environment sensitivity of catalysis

The development of DNA-compatible reaction methodologies is a central theme to advance DNA-encoded screening library technology. Recently, we were able to show that sulfonic acid-functionalized block copolymer micelles facilitated Brønsted acid-promoted reactions such as the Povarov reaction on DNA-coupled starting materials with minimal DNA degradation. Here, the impact of polymer composition on micelle shape, and reaction conversion was investigated. A dozen sulfonic acid-functionalized block copolymers of different molar mass and composition were prepared by RAFT polymerization and were tested in the Povarov reaction, removal of the Boc protective group, and the Biginelli reaction. The results showed trends in the polymer structure-micellar catalytic activity relationship. For instance, micelles composed of block copolymers with shorter acrylate ester chains formed smaller particles and tended to provide faster reaction kinetics. Moreover, fluorescence quenching experiments as well as circular dichroism spectroscopy showed that DNA-oligomer-conjugates, although highly water-soluble, accumulated very effectively in the micellar compartments, which is a prerequisite for carrying out a DNA-encoded reaction in the presence of polymer micelles

Biotin‐Functionalized Block Catiomers as an Active Targeting Approach in Gene Delivery

Abstract Recently, biotin (vitamin H) has been described as a ligand for active targeting and it has been found that many cancer cells overexpress the biotin receptor. In this study a biotin‐conjugated block copolymer, biotin‐poly(2‐ethyl‐2‐oxazoline)‐block‐poly{N '‐[N‐(2‐aminoethyl)‐2‐aminoethyl]aspartamide} (biotin‐pEtOx‐b‐pASP(DEA) is synthesized by a living cationic polymerization of the pEtOx‐block followed by the nucleophilic ringopening polymerization of the pASP‐block. The biotin moiety is coupled to the pEtOx‐b‐pASP precursor by a Cu(I) mediated azide‐alkyne click chemistry and finally, the diethylamine (DEA) side chain is introduced by a polymer analogous reaction. The final polymer P1 formed polyplexes in the presence of plasmid DNA that are characterized with respect to N/P ratio, size, zeta potential, and shape compared to a control polymer P2 without biotin. In addition, HEK293 cells are transfected with these polyplexes and the number of fluorescent HEK293 cells is evaluated to assess the influence of polymer nature on the activity of the micelles. Flow cytometric analysis revealed a significantly higher uptake of the biotin‐PEtOx‐PASP(DEA)/pDNA micelle than the PEtOx‐PASP(DEA)/pDNA micelle against HEK293 cells at a low N/P ratio of 20, consistent with the transfection results whereas at higher N/P ratio no difference can be observed anymore between the two polymers

The Changing System of Scholarly Communication and the Implications for Librarians: Akademik İletişim ve Türkiye Üniversite ve Araştırma Kütüphanecileri

Presented at Seminer@ÖzÜkütüphane: “Bilimsel İletişim ve Üniversite Kütüphaneciliği” on May 8th, 2012 in İstanbulIn recent decades the boundaries of scholarly communication have been progressively expanded as scholars have experienced the advent of technology and particularly the World Wide Web. While the various form of research and the number of outlets multiplying in the field of research, collecting, preserving, and providing access to new age scholarship becomes more and more complex and contentious for university and research libraries. Academic librarians have been at the center of storing and organizing recorded knowledge over the centuries in university and research libraries, and they found themselves playing significant roles at the center of this new scholarly communication context. For instance, one of the newest librarian job titles, “scholarly communication librarian” emerged as a response to this demand among Academic and Research Libraries (ARL). While the job responsibilities of these librarians varies, some of them as follow: coordinating internal library communications on scholarly communication and publishing issues, promoting and managing electronic resources and digital collections, promoting open access, and being library's authority on licensing. The presentation will also touched upon the changing scholarly communication patterns of scientists and the increasing amount of open access journals in the new information era. The lecture will conclude with discussions on what are the action would be needed to embrace the changing face of scholarly communication in Turkish academic and research libraries towards a better future.Teknolojinin ilerlemesi ve özellikle İnternet'in akademisyenlerin hayatına girmesiyle akademik iletişim asırlardır alışılagelmiş formunun dışına çıkmıştır. Özellikle değişen ve gelişen araştırma alanları, araştırmanin iletilebileceği çevrimiçi ve çevrimdışı yayın sahaları, bilginin edinilmesi, saklanması ve kullanıcıya iletimesini üniversite ve araştırma kütüphanelerine kompleks görevler yüklemektedir. Üniversite ve araştırma kütüphanelerinde asırlardır bilgiyi toplayan, saklayan ve kullanıcıya sunan Akademik kütüphaneciler değişen akademik iletişim çerçevesinde kendilerini yeni sorumluluklarla bulmuşlardır. Örneğin Kuzey Amerika akademik ve araştırma kütüphanelerinde bulunan yeni bir kütüphaneci ünvanı da “akademik iletişim kütüphanecisi"dir. Akademik iletişim kütüphanecilerinin meslek tanımları değişmekle birlikte bazılarını şöyle sıralanabilinir: akademik iletişim ve yayıncılıkla ilgili kütüphane içi işlemleri koordine etmek, elektronik kaynakları ve dijital koleksiyonları yönetmek ve kullandırtmak, açık erişimi yönetmek ve kütüphanenin abone olduğu kaynaklarla ilgili lisans anlaşmalarından sorumlu olmak. Bu sunumda bilim insanlarının değişen akademik iletişim paternleri ve gittikçe çoğalan açık erişim yayınları da tartışılacaktır. Ayrica, ders, Türk akademik ve araştırma kütüphanelerindeki bilimsel iletişimin değişen yüzünü kucaklamak için hangi aksiyonun gerekli olacağına ilişkin tartışmalarla sona erecekti

Comparative Studies on the Organogel Formation of a Polyester in Three Different Base Oils by X-ray Analysis, Rheology and Infrared Spectroscopy

High-performance greases typically consist of a base oil and polyurea as a thickener material. To date, few alternatives to polyureas have been investigated. Polyesters could be one such alternative; however, little is known about the gelation of such polyesters because, unlike polyureas, they cannot form hydrogen bonds between the polymer chains. Here, we present studies on the gel formation of a polyester based thickener poly(hexane dodecanoate) with 1-octanol endgroups in three different base oils, i.e., a mineral oil (Brightstock 150), a synthetic Polyalphaolefin (Spectrasyn 40) and castor oil (85 to 90 wt.% ricinoleic acid triglyceride). Small- and wide-angle X-ray scattering measurements indicate a strong interaction of the polyester with castor oil and an increase in the crystalline fraction, with an increasing polymer amount from 5 to 40 wt.%. Moreover, infrared analysis of the polyester in castor oil showed gel formation at a minimum concentration of 20 wt.%. The strong interaction of the polyester with castor oil compared to the other two base oils led to an increase in the yield point γF as a measure of the mechanical stability of the gel, which was determined to be 5.9% compared to 0.8% and 1.0% in Brightstock and Spectrasyn, respectively